1. Field of the Invention
The present invention relates to a resin mold material and a resin mold fabricated with the same, and more particularly to a resin mold material and a resin mold used when a molded product containing a cured resin obtained by curing a liquid resin filling a cavity is manufactured.
2. Description of the Background Art
Conventionally, when a molded product containing a cured resin obtained by curing a liquid resin filling a cavity is manufactured, transfer molding or injection molding has been employed. In such molding, the liquid resin is cured in the cavity while a mold is clamped, and the molded product is taken out after opening the mold. Depending on a type of the cured resin, however, release property of the cured resin from a mold surface may become poor. Accordingly, in order to ensure release of the molded product, an ejector pin is used to press a part of the molded product for ejection thereof. In addition, in some molded products, if voids remain in the cured resin, it may be disadvantageous in terms of reliability or appearance. In such a case, an air vent is provided in the mold so that a gas in the cavity is suctioned through the air vent from the outside of the mold. Discharge of the gas contained in the liquid resin and reduction in pressure in filling the cavity with the liquid resin are thus achieved.
On the other hand, when ejection by means of the ejector pin or suction through the air vent is adopted, a structure of the mold tends to be complicated. In addition, when the molded product is small, excessive force is applied to a part of the molded product by ejection using the ejector pin, resulting in deformation or discoloration of the molded product. As an exemplary manner of resin molding, a chip-type electronic element (hereinafter, referred to as “chip”) such as a semiconductor chip including wire interconnections is accommodated in a cavity, which is in turn filled with the liquid resin in a clamped state, and the resin is cured so as to complete a package. In this case, as the package is made thinner, ejection by means of the ejector pin may cause disconnection of wires and breakage or deformation of the chip and the package.
In order to solve the above-mentioned problems, Japanese Patent Laying-Open Nos. 62-74613 and 8-192438, for example, propose to fabricate a resin mold with a porous body. According to these proposals, suction is carried out through the resin mold fabricated with the porous body, whereby discharge of a gas contained in the liquid resin and reduction in pressure in filling the cavity with the liquid resin are achieved. In addition, when the mold is opened, a high pressure gas such as compressed air is supplied to a mold surface through the resin mold fabricated with the porous body. In this manner, the molded product can be released without using the ejector pin.
A material for the porous body used in the conventional example will now be described. First, Japanese Patent Laying-Open No. 62-74613, in which at least one of the mold (female mold) is formed with porous ceramics in its entirety, discloses mullite-based ceramics as an example of porous ceramics. Meanwhile, Japanese Patent Laying-Open No. 8-192438, in which the mold body, a part of the mold, or a filter layer formed on its surface is fabricated with the porous material, discloses as the porous material, a sintered material obtained by sintering metal powders or ceramics powders.
Here, holes that are formed in the conventional examples will be described. First, Japanese Patent Laying-Open No. 62-74613 disclosing porous ceramics composed of mullite-based ceramics does not mention how the “holes” are. On the other hand, other patent documents such as Japanese Patent Laying-Open Nos. 2000-109374 and 2003-137671 disclose that mullite-based ceramics includes communicating holes linking like a network and communicating in a three-dimensional manner (hereinafter, referred to as “three-dimensional communicating hole”). In addition, according to Japanese Patent Laying-Open No. 8-192438, formed holes are three-dimensional communicating holes, as clearly shown in FIGS. 10 and 19.
The conventional techniques described above, however, suffer from problems due to the fact that the formed holes are three-dimensional communicating holes. First, since the three-dimensional communicating holes have an irregular shape and run in a winding manner, a distance of suction is long and a number of protruded and recessed portions are present on an inner wall. Accordingly, when the gas in the cavity is suctioned through the three-dimensional communicating holes or when a compressed gas is supplied to the mold surface, pressure loss increases. Consequently, the gas cannot completely be removed from the liquid resin, resulting in generation of voids in the molded product. Further, an effect to release the molded product by means of the compressed gas may be lowered. Secondly, since the three-dimensional communicating holes have an irregular shape both in two-dimension and in cross-section, an area occupied by an opening of the three-dimensional communicating hole in the mold surface may be sometimes large and sometimes small. When the opening area is large, the liquid resin is readily introduced in the three-dimensional communicating holes, whereby the cured resin is likely to be caught on the inner wall of the three-dimensional communicating holes in the vicinity of the mold surface. This is particularly the case with the three-dimensional communicating holes extending and spreading two-dimensionally toward a portion located deeper from the mold surface. In other words, because of what is called an anchor effect, adhesion between the mold surface including the inner wall of the three-dimensional communicating holes and the cured resin is increased, resulting in deterioration of release property. Thirdly, as the opening area in the mold surface is not uniform, a two-dimensional shape and an area of the mold surface between the three-dimensional communicating holes are not uniform either. Therefore, even when the mold is manufactured with the same porous material, variation in release property at the mold surface may be considerable.